The present invention relates to a power system used for vehicles operated generally from a sitting position, such as small three-wheeled or four-wheeled vehicles. More particularly, it relates to a variable speed transmission for producing a variable speed by utilizing oil pressure, to power systems which include a unitized combination of an engine and drive train, and to vehicles employing such transmission or combination.
Most larger motor vehicles intended for use as passenger vehicles or for performing certain work functions, such as automobiles, motorcycles, buses, trucks, etc., are provided with power trains which permit the vehicle to maintain a constant velocity while the engine speed is varied to accomplish this purpose. However, in smaller dedicated vehicles which are intended to perform a work function, such as rear engine riders, lawn tractors, front mounted mowers, etc., it is preferred that the engine maintain a constant speed while the vehicle speed varies. This relationship is preferred because, in such vehicles, which generally operate at a relatively slow speed, the work-performing device is connected, either directly or indirectly, to the output end of the crankshaft of the vehicle. Optimum performance of the work-performing device is achieved within a certain rpm range and generally when the power takeoff (hereinafter referred to as PTO) or output end of the crankshaft is rotating at a relatively constant speed. When terrain varies, therefore, a constant vehicle speed is sacrificed for a constant engine speed. This may be accomplished by some form of variable speed transmission.
In a vehicle of conventional design such as, for example, a small four-wheeled cart or buggy as shown in FIG. 1, an engine 10 is arranged in such a way that a crankshaft (output shaft) of the engine extends vertically. Power generated by the engine 10 is transmitted to a trans-axle 16 and a working apparatus such as a lawn mower 18 by means of V-shaped belts 12 and 14, respectively. A driving axle arrangement (not shown) for controlling a variable speed by utilizing oil pressure is incorporated into the trans-axle 16, and rear wheels 19 are rotatably mounted on both ends of the trans-axle 16.
However, in a variable speed transmission comprising the trans-axle 16 and the V-shaped belt 12 used in the four-wheeled buggy as shown in FIG. 1, since the V-shaped belt 12 is twisted in its path, the durability of the V-shaped belt 12 is reduced. Further, in the above variable speed transmission, since the engine 10 and the trans-axle 16 are connected to each other by means of the V-shaped belt 12, the trans-axle 16 cannot be supported floatingly on a chassis of the vehicle and the V-shaped belt 12 tends to become misaligned. Accordingly, it is necessary in the above-described variable speed transmission to use a so-called "rigid axle" in which the trans-axle 16 is rigidly fixed to the vehicle chassis. Further, in the above-described variable speed transmission, since a hydro-static transmission is incorporated into the trans-axle 16 independently of the engine, there is, in many instances, the disadvantage that the temperature of the working oil in the hydro-static transmission is drastically elevated.
Further, in relation to such variable speed transmission, a multiple axis trans-axle has been proposed as described in the Japanese Utility Model Laid-Open No. 87324/1984. However, in the multiple axis trans-axle, since the trans-axle has a plurality of axes, the trans-axle itself is of a large size, thereby requiring a large space for accommodating the trans-axle on the vehicle.
Thus, there is a need for a unitized power system for a vehicle. Preferably, the power system is compact and includes an engine and drive train enclosed in a common housing. A need also exists for a power system which is floatingly supported and eliminates the use of a belt between the engine and transaxle. Vehicles now available also want for a single oil tank or sump which provides oil to the engine and/or the trans-axle as a lubricating oil and to the transmission as an hydraulic fluid.